Fires are not static events. As a fire progresses, it constantly changes as it reaches new fuels, new spaces, and new sources of oxygen. Firefighters making an interior attack in a residence may knock down the fire in a bedroom, then advance the line and face an entirely different situation in a larger open ceiling family room or through a connecting door into a three-car garage. Firefighters tackling a fire in a commercial structure may battle their way through the front offices only to open a door and find that the fire has extended into a large open warehouse space at the rear of the building. Out on the street, the pump operator may engage the deck gun to protect an adjacent building only to discover that wind-driven embers have ignited the roof of a building far across the street.
Whether firefighters are handling a residential fire, commercial fire, or wildland fire, they are often faced with the need to switch streams to handle new situations. Depending on a department’s experience and preference, firefighters may choose a smooth-bore stream for some situations and a fog stream for others. Sometimes they may need to switch back and forth several times as they encounter changing conditions. In really urgent situations, they need to make the switch quickly to protect themselves from escalating fire conditions.
The new co-axial nozzle technology developed by Akron Brass combines the cooling and protection of a true fog stream with the reach and volume of a true smooth-bore stream without compromising the performance of either. It lets firefighters quickly switch from one stream to the other with one control for ease of operation and improved safety.
 Photo courtesy of Akron Brass. |
The co-axial technology allows two separate waterways to fit in one nozzle-one inside the other. The smooth-bore waterway passes directly through the center of the nozzle cavity to produce a solid stream, while the fog waterway passes around the outer portion of the nozzle cavity to emerge in a full fog stream. The technology blends the two nozzle designs into one to achieve the effectiveness of both.
HISTORY OF NOZZLES
The earliest fire nozzles were a smooth-bore style designed to project water to the tops of the tallest buildings-vertical reach was a goal, and considerations such as volume, stream integrity, and cooling protection for the firefighters were also important. Later fog nozzles joined the firefighter’s arsenal of equipment to conserve water, handle certain flammable liquid fires, and protect firefighters from radiant heat. Shortly after that, combination fog/straight stream nozzles became popular because they offered many of the advantages of both types and let firefighters go into action without having to select the appropriate nozzle beforehand.
Some combination nozzles were basically fog nozzles with a sleeve that could be extended forward to deflect the wide-angle fog stream back into a narrower straight stream. The straight stream was more turbulent than the stream from a smooth-bore nozzle, and the pressure drop through the nozzle was significantly greater because of the convoluted path the water had to follow.
Other combination nozzles consisted of a shutoff valve with one or more stacked tips for smooth-bore streams and a separate wide-angle nozzle for fog streams. To switch from one stream to the other, firefighters had to shut down the water flow and manually change the nozzle. This type is still used on many deck guns and monitors.
ThE TECHNOLOGY
To generate a solid, tight smooth-bore stream with excellent reach, the nozzle needs to discharge the water through a straight passageway without obstructions to decrease the turbulence and focus the flow.
To generate a dispersed, wide-fog stream with excellent heat absorption capability, the nozzle needs to discharge the water through an angled passageway with multiple obstructions to increase the turbulence and break up the flow.
These seemingly contradictory requirements can be met with a co-axial nozzle design that directs the solid-bore stream straight through the center of the nozzle and the fog stream around the edges-two passageways, two streams, one nozzle. The center cavity contains a long, straight-bore that smoothes and shapes the flow with a minimum pressure drop. The outer cavity directs the flow around the inner cavity and disperses it out an angled disc.
The success of this design can be found in its performance. For example, with a 15⁄16-inch bore, a 11⁄2-inch handline nozzle can produce a 187-gpm smooth-bore stream with a 139-foot reach at 50-psi nozzle pressure. The high volume, long reach, and low nozzle pressure make it easier for firefighters to quickly knock down large volumes of fire. With the shutoff handle in the fog position, the nozzle produces an adjustable angled 135-gpm fog stream when supplied at 100 psi to finish the job and provide radiant heat protection.
The co-axial design can be used with water, Class A foam, or compressed air foam. It is especially valuable in CAFS applications because the unobstructed smooth-bore passageway produces a tight stream that maintains a good bubble volume with an excellent reach. This allows firefighters to keep a safer standoff distance when making a direct attack or to effectively coat all parts of a threatened structure from a position on the ground in a defensive mode.
In master stream operations, the change from a smooth-bore stream to a fog stream can be made electrically by flipping a switch. This is much quicker and safer than shutting down the flow and having a firefighter climb up onto the apparatus to change nozzles manually as the fire situation changes or as the apparatus is moved from one position to another. ■
■ MARK SANER is the product manager for Akron Brass Company.
